Research Interests

ITCZ/MJO/ENSO in the eastern Pacific

by Chih-Wen Jason Hung

My research interests are primarily in the tropical eastern Pacific, including the seasonal and interannual variations of the ITCZ (Intertropical Convergence Zone) and  MJO (Madden-Julian Oscillation) with El Nino-Southern Oscillation (ENSO).
 

I have worked on the problem of the ITCZ in the past few years, using satellite-based observational datasets to clarify the feature of the ITCZ in the eastern Pacific. Usually, the  NITCZ (Northern Hemisphere ITCZ) stays throughout the year in the northern hemisphere, although it moves back and forth between 5N and 20N. On the other hand, the SITCZ (Southern Hemisphere ITCZ) develops only in March and April, when the sea surface temperature (SST) warms and the surface wind is convergent. During El Nino year, the features of the NITCZ and SITCZ might change: the NITCZ can move cross the equator and combine with the SITCZ (1997-98 El Nino). This causes the absence of the NITCZ in the northern hemisphere, and the strong convection right at the equator in some months. I am very interested in looking at how the seasonal migration of the ITCZ is affected by El Nino, and the air-sea interaction during this movement.

 
I am also interested in MJO behavior in the easter Pacific. The "wet" MJO region as seen in the outgoing longwave radiation (OLR) field moves from western Pacific to eastern Pacific during El Nino, and acts irregularly. The usual "dry" region of the MJO (east of date line in Pacific ocean) can support deep convection when the SST is warmer than normal in the cold tongue region. There are many reports which shows that MJO plays a role in the onset and termination of El Nino, when strong MJOs can reach the eastern Pacific equatorial region. I would like to look at how the different strengths of specific MJOs in different seasons help to build up and terminate the El Nino event, because we have noted that the SSTs of strong El Nino events (such as 1982-83, and 1997-98 El Nino) reach the maximum value in the Northern Hemisphere winter which is also the strongest time for MJO activity in a year. We suggest that although there are many other factors can cause El Nino, the help of MJOs might play a role in its intensification.

 
Finally, I am also working on developing a standard computational scheme for apparent heat source Q1 and apparent moisture sink Q2 and performing intercomparisons of Q1 and Q2 calculated from different reanalysis datasets. This will be useful in demonstrating the interaction between convection and large-scale circulation associated with MJO through the energy transformation involving the available potential energy. Because we will use this standard scheme for long term calculations, the result will help us to realize the relationship between the growth and maintenance of MJO and the interannual variability such as ENSO.

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update: Jan 14 15:58:19 PST 2000